Water electrolysis system

ABSTRACT

A water electrolysis system has a water electrolysis apparatus for electrolyzing pure water, thereby producing hydrogen, a water storage apparatus for separating between oxygen and residual water discharged from the water electrolysis apparatus, thereby storing the water, a water circulation apparatus for circulating the water stored in the water storage apparatus through the water electrolysis apparatus, and a water supply apparatus for supplying the pure water prepared from city water to the water storage apparatus. An inlet is formed at one end of a return pipe to introduce the oxygen and the residual water discharged from the water electrolysis apparatus into a tank, and the position of the inlet is determined such that the inlet is constantly opened in the water stored in the tank.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Applications No. 2009-059371 filed on Mar. 12, 2009 andNo. 2010-013024 filed on Jan. 25, 2010, of which the contents areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a water electrolysis system comprisinga water electrolysis apparatus having current collectors and anelectrolyte membrane disposed therebetween for electrolyzing a water,thereby generating oxygen at the anode side and generating hydrogen atthe cathode side, and a water storage apparatus for separating betweenthe oxygen and the residual water discharged from the water electrolysisapparatus, thereby storing the water.

2. Description of the Related Art

For example, a solid polymer fuel cell produces a direct-currentelectric energy when a fuel gas (a gas mainly composed of hydrogen suchas a hydrogen gas) is supplied to an anode and an oxygen-containing gas(a gas mainly composed of oxygen such as air) is supplied to a cathode.

Conventionally a water electrolysis apparatus is used to produce thehydrogen gas as the fuel gas. The water electrolysis apparatus containsa solid polymer electrolyte membrane (an ion-exchange membrane) fordecomposing water, thereby generating the hydrogen (and the oxygen). Amembrane electrode assembly is prepared by forming an electrode catalystlayer on each surface of the solid polymer electrolyte membrane. Currentcollectors are disposed on the respective sides of the membraneelectrode assembly, making up a unit. The unit is essentially similar instructure to the fuel cells described above.

A plurality of such units are stacked, a voltage is applied across thestack, and water is supplied to the current collector on the anode side.On the anodes of the membrane electrode assemblies, the water isdecomposed to generate hydrogen ions (protons). The hydrogen ionspermeate and move through the solid polymer electrolyte membranes to thecathodes, and bonded with electrons to generate hydrogen. On the anodes,oxygen generated together with the hydrogen ions (the protons) isdischarged together with the residual water from the unit.

For example, a hydrogen storage/power generation system is disclosed assuch a water electrolysis system in Japanese Laid-Open PatentPublication No. 10-068095. As shown in FIG. 11, the hydrogenstorage/power generation system has two water electrolysis apparatuses1, and a pure water supply pipe 2 for supplying pure water is connectedto the water electrolysis apparatuses 1. Pure water stored in anoxygen/pure water tank 3 is supplied through the pipe 2 to an anode ofeach apparatus 1.

Oxygen generated on the anode of the water electrolysis apparatus 1 isintroduced to the oxygen/pure water tank 3 due to the buoyancy. Theoxygen pressure in the oxygen/pure water tank 3 is maintained at apredetermined pressure or less by a pressure control valve 4 a, and theoxygen in the oxygen/pure water tank 3 is discharged through a valve 4b.

Hydrogen generated on the cathode of the water electrolysis apparatus 1is transferred together with the pure water to a hydrogen drain tank 5,and separated from the pure water therein. The hydrogen pressure in thetank 5 is maintained at a predetermined pressure or less by a pressurecontrol valve 6 a, and the hydrogen is discharged through a valve 6 b.

In conventional water electrolysis systems, the hydrogen on the cathodemay be leaked through the solid polymer electrolyte membrane to theanode due to deterioration or failure of a component, etc. Thus, notonly the oxygen and the pure water but also the hydrogen may beintroduced to the oxygen/pure water tank 3. In this case, when the valve4 b is opened, the oxygen and the hydrogen in the tank 3 are dischargedto the outside, so that a continuous hydrogen passage is formed from theoutside through the tank 3 to the water electrolysis apparatus 1.

SUMMARY OF THE INVENTION

An object of the present invention is to solve the above problems,thereby providing a water electrolysis system having a simple structureand which is capable of reliably prevent formation of a continuoushydrogen passage from a water electrolysis apparatus through a waterstorage apparatus in an oxygen discharge path to the outside.

The present invention relates to a water electrolysis system comprisinga water electrolysis apparatus having current collectors and anelectrolyte membrane disposed therebetween for electrolyzing water,thereby generating oxygen at an anode side and generating hydrogen at acathode side, and a water storage apparatus for separating between theoxygen and residual water discharged from the water electrolysisapparatus, thereby storing the water.

The water storage apparatus has a tank for storing the water and aninlet for introducing the oxygen and the residual water discharged fromthe water electrolysis apparatus into the tank. The position of theinlet is determined such that the inlet is constantly opened in thewater stored in the tank.

The present invention further relates to a water electrolysis systemcomprising a water electrolysis apparatus having current collectors andan electrolyte membrane disposed therebetween for electrolyzing a water,thereby generating oxygen at an anode side and generating hydrogen at acathode side, a water storage apparatus for separating between theoxygen and residual water discharged from the water electrolysisapparatus, thereby storing the water, and a water circulation apparatusfor circulating the water stored in the water storage apparatus throughthe water electrolysis apparatus.

The water storage apparatus has a tank for storing the water, an inletfor introducing the oxygen and the residual water discharged from thewater electrolysis apparatus into the tank, and a water return outletfor returning the water in the tank through the water circulationapparatus to the water electrolysis apparatus. The inlet is positionedbelow the water return outlet.

In the present invention, the position of the inlet for introducing theoxygen and the residual water discharged from the water electrolysisapparatus into the tank is determined such that the inlet is constantlyopened in the water stored in the tank. As a result, even when thehydrogen is introduced from the water electrolysis apparatus to the tanktogether with the oxygen and the residual water, the formation of acontinuous hydrogen passage from the water electrolysis apparatusthrough the oxygen discharge path to the outside can be reliablyprevented by the simple structure.

Furthermore, in the present invention, the inlet for introducing theoxygen and the residual water discharged from the water electrolysisapparatus into the tank is positioned below the water return outlet forreturning the water in the tank through the water circulation apparatusto the water electrolysis apparatus. Thus, the inlet is constantly belowthe water surface in the tank. As a result, the formation of acontinuous hydrogen passage from the water electrolysis apparatusthrough the oxygen discharge path to the outside can be reliablyprevented in the simple structure.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which a preferredembodiment of the present invention is shown by way of illustrativeexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural explanatory view showing a waterelectrolysis system according to a first embodiment of the presentinvention;

FIG. 2 is an exploded perspective explanatory view showing a unit cellin the water electrolysis system;

FIG. 3 is a schematic structural explanatory view showing a waterelectrolysis system according to a second embodiment of the presentinvention;

FIG. 4 is a schematic structural explanatory view showing a waterelectrolysis system according to a third embodiment of the presentinvention;

FIG. 5 is a schematic structural explanatory view showing a waterelectrolysis system according to a fourth embodiment of the presentinvention;

FIG. 6 is an explanatory view showing main components of a waterelectrolysis system according to a fifth embodiment of the presentinvention;

FIG. 7 is an explanatory view showing main components of a waterelectrolysis system according to a sixth embodiment of the presentinvention;

FIG. 8 is an explanatory view showing main components of a waterelectrolysis system according to a seventh embodiment of the presentinvention;

FIG. 9 is an explanatory view showing main components of a waterelectrolysis system according to an eighth embodiment of the presentinvention;

FIG. 10 is an explanatory view showing main components of a waterelectrolysis system according to a ninth embodiment of the presentinvention; and

FIG. 11 is a schematic explanatory view showing a hydrogen storage/powergeneration system disclosed in Japanese Laid-Open Patent Publication No.10-068095.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, a water electrolysis system 10 according to a firstembodiment of the present invention comprises a water electrolysisapparatus 12 for electrolyzing water (pure water), thereby producingoxygen and high-pressure hydrogen (whose pressure is higher than normalpressure), a water storage apparatus 14 for separating between theoxygen and residual water discharged from the water electrolysisapparatus 12, thereby storing the separated water, a water circulationapparatus 16 for circulating the water stored in the water storageapparatus 14 through the water electrolysis apparatus 12, a water supplyapparatus 18 for supplying the pure water prepared from city water tothe water storage apparatus 14, a gas-liquid separator 20 for removingwater contained in the high-pressure hydrogen discharged from the waterelectrolysis apparatus 12, a hydrogen dehumidifier 22 for adsorbing andremoving water contained in the hydrogen discharged from the gas-liquidseparator 20, and a controller (a controlling unit) 23.

The water electrolysis apparatus 12 is an apparatus for producing thehigh-pressure hydrogen, and may be for producing normal pressurehydrogen. The normal pressure hydrogen may be defined to include a casein which the generated oxygen and hydrogen have the same pressure.

In the water electrolysis apparatus 12, a plurality of unit cells 24 arestacked. On one end of the unit cells 24 in the stacking direction, aterminal plate 26 a, an insulating plate 28 a, and an end plate 30 a aredisposed in this order toward the outside. On the other end of the unitcells 24 in the stacking direction, a terminal plate 26 b, an insulatingplate 28 b, and an end plate 30 b are disposed in this order toward theoutside. Such plates and unit cells between the end plates 30 a, 30 bare integrally held by fastening.

Terminals 34 a, 34 b extending toward the outside are formed on sidesurfaces of the terminal plates 26 a, 26 b, respectively. The terminals34 a, 34 b are electrically connected to a power source 38 by wirings 36a, 36 b, respectively. The terminal 34 a at the positive electrode(anode) side is connected to the plus pole of the power source 38, andthe terminal 34 b at the negative electrode (cathode) side is connectedto the minus pole of the power source 38.

As shown in FIG. 2, the unit cell 24 has an anode-side separator 44 anda cathode-side separator 46, and a disc-shaped membrane electrodeassembly 42 sandwiched therebetween. The anode-side separator 44 and thecathode-side separator 46 have disc shapes, and may be composed of acarbon member, a steel plate, a stainless steel plate, a titanium plate,an aluminum plate, a plated steel plate, etc. A surface of the metal maybe covered with an anticorrosion-treated metal plate by press molding,or alternatively may be subjected to a surface anticorrosion treatmentafter cutting.

For example, the membrane electrode assembly 42 contains a solid polymerelectrolyte membrane 48 prepared by impregnating a thinperfluorosulfonic acid membrane with water, and further contains ananode-side current collector 50 and a cathode-side current collector 52,which are disposed respectively on the opposite surfaces of the solidpolymer electrolyte membrane 48.

An anode catalyst layer 50 a and a cathode catalyst layer 52 a areformed respectively on the opposite surfaces of the solid polymerelectrolyte membrane 48. For example, the anode catalyst layer 50 a maycomprise a Ru (ruthenium)-based catalyst, and the cathode catalyst layer52 a may comprise a platinum catalyst.

For example, the anode-side current collector 50 and the cathode-sidecurrent collector 52 may be composed of a sintered body of a sphericalatomized titanium powder (a porous conductive material). The anode-sidecurrent collector 50 and the cathode-side current collector 52 each havea flat surface, which is etched after it is cut to shape. The porositiesof the anode-side current collector 50 and the cathode-side currentcollector 52 may be 10% to 50%, more preferably 20% to 40%.

A water supply passage 56 for supplying the water (the pure water), adischarge passage 58 for discharging the oxygen generated by a reactionand the unreacted water (a fluid mixture), and a hydrogen passage 60 fortransferring the hydrogen generated by a reaction are formed in theouter circumferential edge portions of the unit cells 24 continuously inthe stacking direction.

A supply channel 62 a connected to the water supply passage 56 and adischarge channel 62 b connected to the discharge passage 58 are formedon a surface 44 a of the anode-side separator 44 facing the membraneelectrode assembly 42. A first flow field 64 is connected to the supplychannel 62 a and the discharge channel 62 b on the surface 44 a. Thefirst flow field 64 is formed within a surface area of the anode-sidecurrent collector 50, and has a plurality of flow passage grooves,embossed portions, etc.

A discharge channel 66 connected to the hydrogen passage 60 is formed ona surface 46 a of the cathode-side separator 46 facing the membraneelectrode assembly 42. A second flow field 68 is connected to thedischarge channel 66 on the surface 46 a. The second flow field 68 isformed within a surface area of the cathode-side current collector 52,and has a plurality of flow passage grooves, embossed portions, etc.

The outer circumferential edge portions of the anode-side separator 44and the cathode-side separator 46 are integrated by seal members 70 a,70 b. The seal members 70 a, 70 b may comprise a seal material, acushion material, or a gasket material such as EPDM, NBR, fluororubber,silicone rubber, fluorosilicone rubber, butyl rubber, natural rubber,styrene rubber, chloroprene rubber, or acrylic rubber, etc.

As shown in FIG. 1, the water circulation apparatus 16 has a circulationpipe 72 connected to the water supply passage 56 in the waterelectrolysis apparatus 12. The circulation pipe 72 is connected to thebottom of a tank 78 in the water storage apparatus 14, and a circulationpump 74 and an ion exchanger 76 are connected to the circulation pipe72.

One end of a return pipe 80 is connected to the top of the tank 78, andthe other end is connected to the discharge passage 58 in the waterelectrolysis apparatus 12. An inlet 80 a for introducing the oxygen andthe residual water discharged from the water electrolysis apparatus 12into the tank 78 is formed on the one end of the return pipe 80. Theposition of the inlet 80 a is determined such that the inlet 80 a isconstantly opened in the water stored in the tank 78.

A water level detector, such as water level detecting sensors 82 a to 82d, is formed in the tank 78 to detect the water level WS in comparisonwith a predetermined level. A detection signal from the water leveldetecting sensors 82 a to 82 d is inputted into the controller 23.

The water level detecting sensor 82 a is used for detecting whether thewater level WS drops to a predetermined lower level (L), the water leveldetecting sensor 82 b is used for detecting whether the water level WSrises to a predetermined higher level (H), the water level detectingsensor (the lower limit water level detector) 82 c is used for detectingwhether the water level WS drops to a predetermined lower limit level(LL), and the water level detecting sensor 82 d is used for detectingwhether the water level WS rises to a predetermined higher limit level(HH).

The tank 78 is connected to a pure water supply pipe 84 extending fromthe water supply apparatus 18, and to an oxygen discharge pipe 86 fordischarging the oxygen separated from the pure water in the tank 78.

One end of a high-pressure hydrogen pipe 88 is connected to the hydrogenpassage 60 in the water electrolysis apparatus 12, and the other end isconnected to the gas-liquid separator 20. The water contained in thehigh-pressure hydrogen is removed by the gas-liquid separator 20, theresultant hydrogen is dehumidified by the hydrogen dehumidifier 22, andthe obtained dry hydrogen is introduced to a dry hydrogen pipe 90. Adrainpipe 92 is connected to the bottom of the gas-liquid separator 20,and a water discharge valve 94 is connected to the drainpipe 92.

The operation of the water electrolysis system 10 will be describedbelow.

At the start of the operation of the water electrolysis system 10, thepure water prepared from the city water is supplied from the watersupply apparatus 18 to the tank 78 in the water storage apparatus 14.

The water in the tank 78 is supplied by the circulation pump 74 in thewater circulation apparatus 16 through the circulation pipe 72 to thewater supply passage 56 in the water electrolysis apparatus 12.Meanwhile, a voltage is applied to the terminals 34 a, 34 b of theterminal plates 26 a, 26 b by the power source 38 electrically connectedthereto.

As shown in FIG. 2, in each unit cell 24, the water is supplied from thewater supply passage 56 to the first flow field 64 on the anode-sideseparator 44, and is transferred along the anode-side current collector50.

The water is electrically decomposed on the anode catalyst layer 50 a togenerate hydrogen ions, electrons, and oxygen. The hydrogen ionsgenerated by the positive electrode reaction permeate through the solidpolymer electrolyte membrane 48 to the cathode catalyst layer 52 a, andbonded with electrons to produce hydrogen.

Thus, the hydrogen flows through the second flow field 68 between thecathode-side separator 46 and the cathode-side current collector 52. Thehydrogen is under a pressure higher than the pressure in the watersupply passage 56, and thereby can be transferred in the hydrogenpassage 60 and discharged to the outside of the water electrolysisapparatus 12.

A fluid mixture of the oxygen generated by the reaction and theunreacted water flows in the first flow field 64, and is discharged fromthe discharge passage 58 to the return pipe 80 in the water circulationapparatus 16 (see FIG. 1). The oxygen and the unreacted water areintroduced to the tank 78 and separated therein. The separated water isintroduced through the circulation pipe 72 and the ion exchanger 76 tothe water supply passage 56 by the circulation pump 74. The separatedoxygen is discharged through the oxygen discharge pipe 86 to theoutside.

The hydrogen generated in the water electrolysis apparatus 12 istransferred through the high-pressure hydrogen pipe 88 to the gas-liquidseparator 20. Water vapor contained in the hydrogen is removed by thegas-liquid separator 20, and then the resultant hydrogen is dehumidifiedby the hydrogen dehumidifier 22 and introduced to the dry hydrogen pipe90.

In this case, the pressure in the second flow field 68, in which thehydrogen is generated, is higher than that in the first flow field 64,in which the oxygen is generated. Therefore, the hydrogen generated inthe second flow field 68 may readily permeate through the solid polymerelectrolyte membrane 48 to the first flow field 64. The hydrogentransferred to the first flow field 64 is discharged to the return pipe80 and introduced to the tank 78 together with the unreacted water andthe oxygen.

In the first embodiment, the inlet 80 a formed at the one end of thereturn pipe 80 is constantly opened in the water stored in the tank 78.The inlet 80 a is constantly below the water level WS.

Thus, even when the hydrogen is introduced from the water electrolysisapparatus 12 to the tank 78 together with the oxygen and the residualwater, the formation of a continuous hydrogen passage from the waterelectrolysis apparatus 12 through the oxygen discharge path (i.e., thereturn pipe 80, the internal space of the tank 78, and the oxygendischarge pipe 86) to the outside can be reliably prevented in thesimple structure.

In addition, in the first embodiment, the tank 78 has the water leveldetecting sensors 82 a to 82 d for detecting the water level WS in thetank 78 in comparison with the predetermined levels.

Specifically, the water level detecting sensor 82 a is used fordetecting whether the water level WS drops to the predetermined lowerlevel (L). When the drop of the water level WS to the lower level (L) isdetected, the pure water addition from the water supply apparatus 18 tothe tank 78 is instructed by the controller 23. Then, the water leveldetecting sensor 82 b is used for detecting whether the water level WSrises to the predetermined higher level (H). When the rise of the waterlevel WS to the higher level (H) is detected, the pure water additionfrom the water supply apparatus 18 to the tank 78 is stopped by thecontroller 23.

Furthermore, the water level detecting sensor 82 c is used for detectingwhether the water level WS drops to the predetermined lower limit level(LL). When the drop of the water level WS to the lower limit level (LL)is detected, the operation of the water electrolysis system 10 isstopped by the controller 23 due to system malfunction. Further, thewater level detecting sensor 82 d is used for detecting whether thewater level WS rises to the predetermined higher limit level (HH). Whenthe rise of the water level WS to the higher limit level (HH) isdetected, the operation of the water electrolysis system 10 is stoppedby the controller 23 due to system malfunction.

The desired water electrolysis treatment can be efficiently carried outin the water electrolysis system 10 successfully in this manner.

FIG. 3 is a schematic structural explanatory view showing a waterelectrolysis system 100 according to a second embodiment of the presentinvention.

The common components in the water electrolysis system 10 of the firstembodiment and the water electrolysis system 100 of the secondembodiment are represented by the same numerals, and duplicateexplanations therefor are omitted. Also in third and other followingembodiments, the duplicate explanations are omitted in the same manner.

The water electrolysis system 100 has a water storage apparatus 102, andan inlet 80 a formed at one end of a return pipe 80 is opened in thebottom of a tank 104 in the water storage apparatus 102.

FIG. 4 is a schematic structural explanatory view showing a waterelectrolysis system 110 according to a third embodiment of the presentinvention.

The water electrolysis system 110 has a water storage apparatus 112, andan inlet 80 a formed at one end of a return pipe 80 is opened in a sidesurface of a tank 114 in the water storage apparatus 112.

In the second and third embodiments, the inlets 80 a are constantlypositioned below the water level WS. Thus, the second and thirdembodiments have the same advantageous effects as the first embodiment.

FIG. 5 is a schematic structural explanatory view showing a waterelectrolysis system 120 according to a fourth embodiment of the presentinvention.

The water electrolysis system 120 has a water storage apparatus 122, andan inlet 80 a formed at one end of a return pipe 80 is opened in thebottom of a tank 124 in the water storage apparatus 122. A water returnoutlet 72 a of a circulation pipe 72 is formed in a side surface of thetank 124. A partition plate 126 is disposed in the tank 124, whereby theoxygen (and the hydrogen) introduced from the inlet 80 a of the returnpipe 80 to the tank 124 is prevented from being sucked from the waterreturn outlet 72 a.

In the fourth embodiment, the inlet 80 a for introducing the oxygen andthe residual water discharged from the water electrolysis apparatus 12into the tank 124 is positioned below the water return outlet 72 a forreturning the water in the tank 124 to the water electrolysis apparatus12.

The inlet 80 a is constantly positioned below the water level WS in thetank 124. As a result, the formation of a continuous hydrogen passagefrom the water electrolysis apparatus 12 through the oxygen dischargepath to the outside can be reliably prevented in the simple structure.Thus, the fourth embodiment has the same advantageous effects as thefirst to third embodiments.

FIG. 6 is an explanatory view showing main components of a waterelectrolysis system 130 according to a fifth embodiment of the presentinvention.

The water electrolysis system 130 has a water storage apparatus 132. Aninlet 80 a of a return pipe 80 and a water return outlet 72 a of acirculation pipe 72 are opened in the bottom of a tank 134 in the waterstorage apparatus 132. A partition wall member 136 is disposed in thetank 134.

The partition wall member 136 is a plate-like member, and extendsupwardly above a predetermined higher limit level (HH) in the tank 134.In a lower portion of the partition wall member 136, a lower opening 138is formed and is in communication with the water return outlet 72 a. Inor around an upper portion of the partition wall member 136, an upperopening 140 is formed and is in communication with a discharge outlet 86a of an oxygen discharge pipe 86. The upper opening 140 may be providedin the form of a hole or holes and the like in the partition wall member136. Otherwise, the upper opening 140 may be provided in the form of agap or gaps and the like between an upper end of the partition wallmember 136 and a top plate of the tank 134.

When the unreacted water and the oxygen together with the hydrogen areintroduced into the tank 134 through the inlet 80 a through the returnpipe 80, the liquid surface of the water tends to be unstable due to thegas (oxygen and hydrogen) in the water.

In the fifth embodiment having the above structure, since the partitionwall member 136 is formed in the tank 134, it is possible to reliablyprevent the liquid surface on a part of the tank 134 having water leveldetecting sensors 82 a to 82 d from ruffling. Accordingly, advantageouseffects can be obtained such that an error in detecting the position ofliquid surface, i.e., the water level WS by the water level detectingsensors 82 a to 82 d can be prevented as much as possible.

Incidentally, the gas components introduced from the inlet 80 a into thetank 134 are discharged from the upper opening 140 around the upperportion of the partition wall member 136 to the discharge outlet 86 a ofthe oxygen discharge pipe 86. On the other hand, the water introducedfrom the inlet 80 a into the tank 134 is supplied from the lower opening138 in the lower portion of the partition wall member 136 to the part ofthe tank 134 having the water level detecting sensors 82 a to 82 d.

In this case, an upper end of the partition wall member 136 ispositioned above the higher limit level (HH). Therefore, it is possibleto reliably prevent the water from flowing out from the part having theinlet 80 a through the upper opening 140.

FIG. 7 is an explanatory view showing main components of a waterelectrolysis system 150 according to a sixth embodiment of the presentinvention.

The water electrolysis system 150 has a water storage apparatus 152. Aplurality of, e.g., two partition wall members 136, 156 are disposed ina tank 154 of the water storage apparatus 152.

The partition wall members 136, 156 are positioned substantially inparallel to each other. The partition wall member 156 is in contact witha top plate of the tank 154 and is positioned upwardly away from thebottom of the tank 154 by a predetermined distance. In an upper portionof the partition wall member 156, an upper opening 158 is formed fordischarging the gas components from a discharge outlet 86 a of an oxygendischarge pipe 86.

In the sixth embodiment having the above structure, the inside of thetank 154 is divided into three parts 160 a, 160 b, 160 c by the twopartition wall members 136, 156. Thus, the water and the oxygen flowingback into the tank 154 from an inlet 80 a of a return pipe 80, are firstintroduced into the first part 160 a for gas-liquid separation.

The separated gas components are discharged from the discharge outlet 86a through and around the upper portion of the partition wall member 136and the upper opening 158 of the partition wall member 156. On the otherhand, the water moves from the first part 160 a to the second part 160 bthrough a lower opening 138. Thereafter, the water is supplied to thethird part 160 c from below the partition wall member 156.

Accordingly, even if the gas components in the water supplied in thefirst part 160 a causes the ruffling of the liquid surface, the rufflingof the liquid surface is reduced in the second part 160 b and theruffling is further prevented as much as possible in the third part 160c, advantageously. Furthermore, even if the water flows out from aroundthe upper portion of the partition wall member 136 to the second part160 b, the ruffling of the liquid surface is not caused in the thirdpart 160 c because of a liquid-surface-ruffling prevention function ofthe partition wall member 156.

In the sixth embodiment, the inlet 80 a is opened in the bottom of thetank 154. The present invention, however, is not limited to thisarrangement. For example, the inlet 80 a may be opened in the lower sidesurface of the tank 154 near the bottom (see dashed double-dotted linesin FIG. 7). On the other hand, a water return outlet 72 a of acirculation pipe 72 is opened in the bottom of the tank 154. Otherwise,as shown in FIG. 5, for example, the water return outlet 72 a may beformed in a lower side surface of the tank 154 near the bottom.

FIG. 8 is an explanatory view showing main components of a waterelectrolysis system 170 according to a seventh embodiment of the presentinvention.

The water electrolysis system 170 has a water storage apparatus 172.Partition wall members 176 a, 176 b are disposed in a tank 174 of thewater storage apparatus 172. The partition wall members 176 a, 176 b areprovided so that an inlet 80 a of a return pipe 80 is sandwiched betweenthem. On upper ends of the partition wall members 176 a, 176 b, a lidmember 178 is integrally disposed. In an upper portion of the partitionwall member 176 a, an upper opening 180 a is formed, and a lower opening180 b is formed in a lower portion of the partition wall member 176 b.

In the seventh embodiment having the above structure, the inlet 80 a ofthe return pipe 80 is opened between the pair of partition wall members176 a, 176 b. The ruffling of the liquid surface between the partitionwall members 176 a, 176 b does not affect other parts in the tank 174.

Also, since the lid member 178 is disposed on the upper ends of thepartition wall members 176 a, 176 b, water does not splash in theoutside of the partition wall members 176 a, 176 b. Thus, the seventhembodiment has the same advantageous effects as the fifth and sixthembodiments.

FIG. 9 is an explanatory view showing main components of a waterelectrolysis system 190 according to an eighth embodiment of the presentinvention.

The water electrolysis system 190 has a water storage apparatus 192. Apair of partition wall members 196 a, 196 b is disposed in a tank 194 ofthe water storage apparatus 192. The partition wall members 196 a, 196 bare integrally formed by a top plate member 196 c. In a space defined bythe partition wall members 196 a, 196 b and the top plate member 196 c,an inlet 80 a of a return pipe 80 is opened. In an upper portion of thepartition wall member 196 a, an upper opening 198 a is formed, and alower opening 198 b is formed in a lower portion of the partition wallmember 196 b.

FIG. 10 is an explanatory view showing main components of a waterelectrolysis system 200 according to a ninth embodiment of the presentinvention.

The water electrolysis system 200 has a water storage apparatus 202. Twopartition wall members 206, 208 are disposed in a tank 204 of the waterstorage apparatus 202. An inlet 80 a of a return pipe 80 is openedbetween the partition wall members 206, 208. In a lower part of thepartition wall member 208, a lower opening 210 is formed. There is anopen space above the upper ends of the partition wall members 206, 208,so that an upper opening 212 is formed between a top plate of the tank204 and the upper ends of the partition wall members 206, 208.

Thus, the eighth and ninth embodiments with the above structures havesubstantially the same advantageous effects as the seventh embodimentshown in FIG. 8.

Although certain preferred embodiments of the present invention havebeen shown and described in detail, it should be understood that variouschanges and modifications may be made therein without departing from thescope of the appended claims.

1. A water electrolysis system comprising: a water electrolysisapparatus including current collectors and an electrolyte membranedisposed therebetween for electrolyzing water, thereby generating oxygenat an anode side and generating hydrogen at a cathode side; and a waterstorage apparatus for separating between the oxygen and residual waterdischarged from the water electrolysis apparatus, thereby storing thewater, wherein the water storage apparatus includes a tank for storingthe water and an inlet for introducing the oxygen and the residual waterdischarged from the water electrolysis apparatus into the tank, and theposition of the inlet is determined such that the inlet is constantlyopened in the water stored in the tank.
 2. A water electrolysis systemaccording to claim 1, further comprising a water circulation apparatusfor circulating the water stored in the water storage apparatus throughthe water electrolysis apparatus.
 3. A water electrolysis systemaccording to claim 1, further comprising a water supply apparatus forsupplying the water to the water storage apparatus, wherein the waterstorage apparatus includes a water level detector for detecting a waterlevel in the tank in comparison with a predetermined level, and thewater supply from the water supply apparatus to the water storageapparatus is controlled based on a detection signal from the water leveldetector.
 4. A water electrolysis system according to claim 3, whereinthe water storage apparatus includes a lower limit water level detectorfor detecting the water level in the tank in comparison with apredetermined lower limit level, and operation of the water electrolysisapparatus is stopped based on a detection signal from the lower limitwater level detector.
 5. A water electrolysis system according to claim1, wherein the water storage apparatus includes a partition wall memberdisposed in the tank, and an upper end of the partition wall member ispositioned above a predetermined higher limit level in the tank.
 6. Awater electrolysis system according to claim 5, wherein the tankincludes: a water return outlet for returning the water in the tank tothe water electrolysis apparatus through the water circulationapparatus; and a discharge outlet for discharging a separated gascomponent, and wherein a lower opening is formed in a lower portion ofthe partition wall member and is in communication with the water returnoutlet, and an upper opening is formed around an upper portion of thepartition wall member and is in communication with the discharge outlet.7. A water electrolysis system according to claim 5, wherein a pluralityof the partition wall members are provided.
 8. A water electrolysissystem comprising: a water electrolysis apparatus including currentcollectors and an electrolyte membrane disposed therebetween forelectrolyzing water, thereby generating oxygen at an anode side andgenerating hydrogen at a cathode side, a water storage apparatus forseparating between the oxygen and residual water discharged from thewater electrolysis apparatus, thereby storing the water, and a watercirculation apparatus for circulating the water stored in the waterstorage apparatus through the water electrolysis apparatus, wherein thewater storage apparatus includes a tank for storing the water, an inletfor introducing the oxygen and the residual water discharged from thewater electrolysis apparatus into the tank, and a water return outletfor returning the water in the tank through the water circulationapparatus to the water electrolysis apparatus, and the inlet ispositioned below the water return outlet.
 9. A water electrolysis systemaccording to claim 8, wherein a partition plate is formed in the tank toprevent the oxygen and the hydrogen introduced from the inlet into thetank from being sucked into the water return outlet.